1. Field of the Invention
The present invention relates to the treatment of human subjects for hypovolemic shock by rapid infusion of physiologic solutions into the human body which have been warmed to normothermic temperature prior to their infusion into the human body.
2. Description of the Prior Art
Treatment of hypovolemic shock requires rapid volume replacement and maintenance of normothermic temperature in vital organs of the human body. In order to resuscitate a victim in hypovolemic shock, secondary to traumatic or intraoperative hemorrhage, physiologic solutions including blood products, synthetic colloids, and crystalloids must be rapidly infused into the body. These physiologic solutions are presently introduced through a multitude of venipunctures cannulated with 18-gauge or larger internal diameter catheters. The rapidly infused physiologic solutions should also be warmed to normothermic temperature in order to maintain normothermic temperature in the vital organs of the body and prevent transfusion-induced hypotermia. Present methods of fluid administration achieve infusion rates which are too slow. Present blood warming methods demonstrate an inherent resistance to infusion flow, which does not allow adequate flow rates for optional hypovolemic shock treatment.
Banked blood is stored in a refrigerated environment at a temperature of 4 degrees Centigrade. For years, banked blood has been transfused into human subjects cold as it came from the storage refrigerator. Patients who receive as little as two units of cold banked blood tend to become hypothermic. The first major organ to be exposed to the stream of cold bank blood is the heart. Heart rate, blood pressure, cardiac output, and coronary blood flow all fall progressively as body temperature drops. The heart tends to fail during cooling either suddenly because of ventricular fibrillation, or gradually because of ischemia. C. P. Boyan, "Cold or Warmed Blood for Massive Transfusions." Annals of Surgery, 160: 282-286 (1964). In a study of 154 hypovolemic shock victims, Dr. Boyan found that there was a 58 percent mortality rate among patients receiving cold infusion of resuscitation fluids. There was a 6 percent mortality rate among patients receiving normothermic massive transfusions. Id. at pp. 284-286. However, the Volume Replacement System used in that study was deficient due to its large priming volume requirement, its lack of controlled warming capability, and its less than optimal infusion delivery rate.
Fluid replacement through peripheral veins has been the standard method of volume resuscitation. Cold bank blood and blood products are infused into the patient through a "Y" type blood solution administration set. The blood solution administration set uses a 200 micron filter and PVC tubing which is 84 inches long and has a 0.06 inch internal diameter. A crystalloid solution administration set is sometimes used. It employs PVC tubing which is 93 inches long and has a 0.06 inch internal diameter. A 16-gauge vein catheter is attached to each blood or crystalloid solution administration set, and is inserted directly into the vein. Fluids are kept in storage bags which are elevated above the solution administration sets. Each solution administration set has a hollow spike connector, which is used to connect it to the storage bag. Gravity induces the fluid to flow from the storage bag through the spike connector into the solution administration sets. The solution administration sets are elevated above the patient, and gravity induces the fluid to flow through the set to the attached vein catheters. Fluid then enters the patient through the catheter into the venous access sites.
Certain disadvantages are inherent in the use of solution administration sets to infuse cold bank blood and blood products for volume resuscitation. First, it is likely that the patient will experience transfusion-induced hypothermia. Rapid body cooling during the treatment of hypovolemic shock is associated with cardiac arrest. Second, the PVC tubing used in prior fluid administration resists flow and delays delivery of fluid to central compartments. Tubing which has a 0.06 inch internal diameter, and which has a long length of 84 inches or more, cannot deliver fluids to a patient at an infusion rate needed for successful resuscitation from hypovolemic shock. The infusion rate must be approximately 1500 milliliters per minute or greater. As a result the infusion rate of replacement fluids to the patient may not approximate the rate of loss. Unless such an infusion rate is achieved, the patient cannot be resuscitated. Also, in a hypotensive, hypovolemic shock victim, peripheral veins are not always easily accessible for mutliple venipunctures. J. Scott Millikan, Thomas L. Cain, and John Hansbrough, "Rapid Volume Replacement for Hypovelomic Shock: A Comparison of Techniques and Equipment." Journal of Trauma, 24: 428- 431 (1984). This procedure requires multiple venous access sites to connect several infusion systems for adequate volume replacement. Initiating such treatment is timeconsuming, and the delay incurred contributes significantly to the mortality rate among hypovolemic shock victims. During the time taken to initiate treatment, physiologic alterations produced by massive hemorrhage progress to an irreversable state, making death inevitable.
A fluid warming coil is used in volume resuscitation. A device of this type is described and illustrated in U.S. Pat. No. 3,472,369 to Samuel J. Schuster. The fluid warming coil described in the Schuster patent consists of PVC tubing which is 34 feet long. It also has a 0.06 inch internal diameter. The device described in the Schuster patent must also be immersed in a tank of warm water for heat transfer. Cold bank blood and blood products are warmed by flowing through the plastic tubing after it has been immersed in warm water.
Certain disadvantages are inherent in the device described in the patent. First, it does not allow measurement of blood temperature. It therefore does not facilitate controlled warming of cold blood and blood products to normothermic temperature. This is critical in the prevention of hypothermia, or of hypertermia which may cause red blood cell hemolysis and platelet denaturation and can thereby cause death. Second, the coil length and internal diameter resists blood flow such that the coil cannot warm blood at maximal infusion rates of 1500 milliliters per minute or greater. Use of the coil where massive hemorrhage has occurred therefore reduces the patient's likelihood of resuscitation from hypovolemic shock.
Consequently, a need exists for improvements in the infusion of normothermic physiologic solutions into human subjects experiencing hypovolemic shock.